import sys; input=sys.stdin.readline
MOD = 998244353

N = int(input())
L, R = [None]*N, [None]*N
for i in range(N):
  L[i], R[i] = map(int, input().split())
  L[i] -= 1

inv2 = pow(2, -1, MOD)
ans = 1
for i in range(1, N):
  sm = 0
  if L[0] >= R[i]: continue
  if R[0] < L[i]:
    ans += 1
    continue
  if L[0]<L[i]: sm += (R[i]-L[i])*(L[i]-L[0])
  if R[0]<R[i]: sm += (R[0]-L[0])*(R[i]-R[0])
  sm -= max(0, R[i]-R[0])*max(0, L[i]-L[0])
  l, r = max(L[0], L[i]), min(R[0], R[i])
  sm = (sm+(r-l)*(r-l-1)*inv2)%MOD
  sm = (sm*pow(R[i]-L[i], -1, MOD))%MOD
  sm = (sm*pow(R[0]-L[0], -1, MOD))%MOD
  ans += sm
ans %= MOD
print(ans)